Microbial Risk Assessment of Mature Compost from Human Excreta, Cattle Manure, Organic Waste, and Biochar
, Daniela Castro-Herrera 2, Fantaw Yimer 3, Menfese Tadesse 3, Dong-Gill Kim 3, Katharina Prost 2, Nicolas Brüggemann 2 and Elisabeth Grohmann 1,*Round 1
Reviewer 1 Report
It's a well-written article. I have a few questions/ comments.
1. are there countries/ regions in the world that already uses human excreta as fertilizer? If yes - add some information, if no to the best of the author's knowledge, mention so.
2. Methods & Materials, Lines 68-79. - Is there a reason not to have a sample with just sawdust? What's your baseline?
3. How does the nutrient content as in fertilizer quality varies between these different samples?
Author Response
Dear Reviewer,
Thank you for the critical reading of our manuscript and your thoughtful comments that we would like to address step by step in the following.
- are there countries/ regions in the world that already uses human excreta as fertilizer? If yes - add some information, if no to the best of the author's knowledge, mention so.
Response: We have added a paragraph on this topic to the introduction in lines 54-65 in the version with track changes.
- Methods & Materials, Lines 68-79. - Is there a reason not to have a sample with just sawdust? What's your baseline?
Response: Thank you for the careful reading of our manuscript. It is not usual in composting trials to conduct controls with just one of the feedstock materials (e.g., [1]–[4]). The reason is that composting as a complex process requires a suitable combination of certain parameters, such as moisture contents between 45-60 % and C:N ratios of 25:1 to 35:1 [5]. To use only sawdust as feedstock material, the initial mixture would have to be altered to achieve a functioning composting process. Its usefulness as a control would have been debatable. Therefore, in our trial cattle manure served as a control. To adjust the conditions, cattle manure was mixed with the same sawdust used for the dry toilets. We have emphasized this in lines 97-99.
We used threshold values for indicator pathogens that are implemented in legal regulations for organic fertilizers as a reference for the sanitation success of the composting process.
- How does the nutrient content as in fertilizer quality varies between these different samples?
Response: The assessment of nutrients (C, N, P, K, Ca, Mg, micronutrients) was part of a previous publication on the same composting trial [6]. Overall, nutrient losses during composting were low. Most of the nitrogen from the feedstock materials was conserved during composting with best results in the CM+BC treatment, where losses were completely prevented compared with the control treatment (CM). Differences between biochar and control treatments were observed for TOC, which was higher in the BC treatments (51.9 % and 45 % in HM+BC and CM+BC, respectively, as compared with 38.3 % (HM) and 32.1 % (CM)). Moreover, TOM exhibited 18-23 % and TOC 33-42% less losses in the BC treatments. Decreases of extractable NO3- were significantly reduced by 32-36 % in the BC treatments as compared with the controls. P and K contents were not influenced by the addition of biochar, and losses were overall low. Ca, Mg, Zn, Cu, Fe, B, and Mo contents were also not found to be influenced by biochar, but Mn contents were higher in the BC treatments (230 and 323 g/kg in HM+BC and CM+BC, respectively, as compared with 58 and 86 g/kg in HM and CM). Exact values for the mentioned nutrients can be found in Castro-Herrera et al. (2021, Table 1). We have highlighted this in line 88.
Literature
[1] Y. Gao et al., “Full-Scale of a Compost Process Using Swine Manure, Human Feces, and Rice Straw as Feedstock,” Front. Bioeng. Biotechnol., vol. 10, Jul. 2022, doi: 10.3389/fbioe.2022.928032.
[2] Q. Li, X. C. Wang, H. H. Zhang, H. L. Shi, T. Hu, and H. H. Ngo, “Characteristics of nitrogen transformation and microbial community in an aerobic composting reactor under two typical temperatures,” Bioresour. Technol., vol. 137, pp. 270–277, Jun. 2013, doi: 10.1016/j.biortech.2013.03.092.
[3] S. Hashemi, S. Boudaghpour, and M. Han, “Evaluation of different natural additives effects on the composting process of source separated feces in resource-oriented sanitation systems,” Ecotoxicol. Environ. Saf., vol. 185, p. 109667, Dec. 2019, doi: 10.1016/j.ecoenv.2019.109667.
[4] Y. M. Piceno et al., “Bacterial community structure transformed after thermophilically composting human waste in Haiti,” PLoS One, vol. 12, no. 6, p. e0177626, Jun. 2017, doi: 10.1371/journal.pone.0177626.
[5] P. Román, M. M. Martínez, and A. Pantoja, “Farmer`s compost handbook. Experiences in Latin America,” Santiago, 2015.
[6] D. Castro‐Herrera et al., “Nutrient dynamics during composting of human excreta, cattle manure, and organic waste affected by biochar,” J. Environ. Qual., pp. 1–14, 2021, doi: 10.1002/jeq2.20312.
Sincerely,
Katharina Werner
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Authors, after reviewing your ms. I believe that your ms is a lot for communication and small for article. You must add or remove. In the ms you must add a staistical part that is missing and some picture or figure about Ascaris lumbricoides eggs. Please for the nematode add in the first time full classification. The presentation and the originality is low rate.
Author Response
Dear Reviewer,
Thank you for the critical reading of our manuscript and your thoughtful comments that we would like to address step by step in the following.
Dear Authors, after reviewing your ms. I believe that your ms is a lot for communication and small for article. You must add or remove.
Response: As suggested, we have shortened the manuscript in the discussion (lines 235-238, 241-244, 253-257, 273-279, 291-294 in the file with track changes).
In the ms you must add a staistical part that is missing and some picture or figure about Ascaris lumbricoides eggs. Please for the nematode add in the first time full classification. The presentation and the originality is low rate.
Response: Thank you for pointing this out. We have included a section on the statistics used in the M&M section (chapter 2.4, lines 175-183). A figure showing the Mini-FLOTAC counting chamber and microscopical images of Ascaris eggs as an example were included in the M&M (chapter 2.3, Figure 2, lines 171-174).
In line 22 in the abstract and line 70 in the introduction, we gave the full name (genus and species) of the nematode, as well as in the headings of the subsections. In addition, we included the phylum and common name in the introduction (lines 69 and 71).
The presentation was improved by adding a picture of Ascaris eggs in the M&M (Fig. 2), as well as a chapter for the statistical evaluation of the data (chapter 2.4, lines 175-183). In response to the other Reviewers, the experimental scheme was presented in an additional table (Table 1, lines 113-126), and the Results section was amended by a second data table for the Ascaris egg count (Table 3, lines 206-211).
Sincerely,
Katharina Werner
Author Response File: Author Response.pdf
Reviewer 3 Report
The review concerned the Communication Microbial risk assessment of mature compost from human excreta, cattle manure, organic waste, and biochar.
Abstract spelled correctly.
As for the introduction, in my opinion, the issues related to microbiological hazards should be described in more detail.
The material and methods chapter is not entirely clear to me. The scheme of the experiment and variants can be presented in the table. Another thing is to cite literature for research methods. You need to refer to the cited articles and look for the methods cited by the authors. In my opinion, the methods used should be described in detail in this chapter. In my opinion, this should be improved.
Research results chapter. The results of the research were presented using 1 table. Three microbiological hazards have been described.
The discussion chapter is the longest chapter in the article, but it should be proportionate to the results of the research. Therefore, it is absolutely necessary to extend the research results chapter.
Considering the form that this is not an article but a Communication, please improve the research methods and improve the presentation of research results.
Author Response
Dear Reviewer,
Thank you for the critical reading of our manuscript and your thoughtful comments that we would like to address step by step in the following.
As for the introduction, in my opinion, the issues related to microbiological hazards should be described in more detail.
Response: Thank you for your comment. We have added a section on the microbiological hazards of fecal material used for fertilization to the introduction (lines 42-48 in the manuscript with track changes).
The material and methods chapter is not entirely clear to me. The scheme of the experiment and variants can be presented in the table. Another thing is to cite literature for research methods. You need to refer to the cited articles and look for the methods cited by the authors. In my opinion, the methods used should be described in detail in this chapter. In my opinion, this should be improved.
Response: Thanks for your suggestions. A scheme for the experimental set-up was included in the M&M section (Table 1, lines 113-126).
Thank you for pointing out the missing literature. We have complemented the text with the reference for the experimental procedure used for the isolation of Ascaris eggs (lines 163-164). The literature cited for the detection of E. coli and Salmonella, however, contains the full description of the methods that we have used. Instead of referring to our previous publication, we described the protocol in detail in the revised manuscript (lines 134-159).
Research results chapter. The results of the research were presented using 1 table. Three microbiological hazards have been described.
Response: Thank you for your comment. We have included a second table in the results section (Table 3, lines 206-211) to show the results of the Ascaris egg count.
The discussion chapter is the longest chapter in the article, but it should be proportionate to the results of the research. Therefore, it is absolutely necessary to extend the research results chapter.
Response: Thank you for pointing this out. We agree that there was an imbalance in the lengths of Results and Discussion. As stated above, we have included a second table in the results section. In addition, the discussion was shortened to reduce the gap in lengths between the two chapters (lines 235-238, 241-244, 253-257, 273-279, 291-294).
Considering the form that this is not an article but a Communication, please improve the research methods and improve the presentation of research results.
Response: The presentation was improved by adding a picture of Ascaris eggs in the M&M (Fig. 2), as well as a chapter for the statistical evaluation of the data (chapter 2.4, lines 175-183). The experimental scheme was presented in an additional table (Table 1, lines 113-126), and the Results section was amended by a second data table for the Ascaris egg count (Table 3, lines 206-211).
Sincerely,
Katharina Werner
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
I believe that is ok now.
